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AlN containing composite - a white light emitter
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Dr.habil.phys. B. Bērziņa (Wide Band Material Laboratory, ISSP)

Researchers of Wide Band Materials, ISSP, are studying spectral properties of nitrides (AlN, BN), oxides (Al2O3, ZnO) and other materials (C, diamonds), measuring spectra of photoluminescence and its excitation as well as absorption spectra in wide spectral range including UV, visible and IR light. Spectral measurements are performed in the 8-300 K temperature range. The aim of the studies is elucidating of luminescence processes and the mechanisms caused by excitation of material host and defects, as well as estimation of material practical application in various devices.

Spectral properties of AlN have been studied in the laboratory for many years, using samples of different structure: AlN ceramics, powders of macro size, nanotips, nanorods and nanopowder. It was found that luminescence of these materials is characterized with two blue luminescence bands (~400 nm and 480 nm) caused by presence of oxygen-containing native defects. Decrease of AlN grain size leads to the increase of relative contribution of the 480 nm band. In AlN nanopowders only the 480 nm band is observed. Besides, it is possible to dope material with different impurities, which have their own characteristic luminescence. For example, Mn impurity is characterized with a red band (600 nm), Tb - with a green band (~550 nm).

It is possible to use luminescence of different colors to produce a white light emitter. It is known that white light is created by mixing light beams of three colors – blue, green (or yellow) and red. The proposed material for a white light emitter contains a mixture of AlN, AlN-Tb and AlN-Mn nanopowders integrated in PMMA (polymethyl methacrylate) matrix forming a composite. Optimal proportions of the components were chosen basing on the results of spectral measurements. Studies resulted in creation of the AlN containing composite – white light emitter, which is excited by UV light in 250-300 nm spectral range and could be used in luminescence lamps.

The results of this study are summarized in a submitted European patent.